Kingdom Animalia

Kingdom Animalia

1. General Measures of Complexity

a. Embryonic development

i. The zygote becomes an adult through embryonic development

ii. The cells of the zygote divide to form a hollow ball of cells called a blastula. This ball folds inward to form a gastrula during gastrulation. The opening of the gastrula becomes either the mouth of anus.

iii. All cells of the adult organism can be traced to one of the three germ layers. Some animals have only the inner and outer germ layers but more complex animals have mesoderm as well.

(1) Ectoderm - the inner layer gives rise to the outer covering of the animal and the nervous system.

(2) Mesoderm - gives rise to muscles, skeleton, circulatory system, kidney, reproductive system

(3) Endoderm - gives rise to digestive tract and associated organs

b. Symmetry

i. Asymmetry - The simplest animals have no symmetry.

ii. Radial - The axis of symmetry goes through the center of the animal from top to bottom. These animals are more complex than those with no symmetry.

iii. Bilateral - The axis of symmetry is through the middle of the animal from head to tail. Bilateral organisms exhibit right and left halves, mirror images to each other.

2. Phylum Porifera

a. General

i. Sponges are the simplest of animals

ii. Lack mesoderm, symmetry, and tissues

iii. Some cells are specialized but not organized into tissues

iv. The body is little more than a mass of specialized cells

v. Adults are sessile and remain anchored to the ocean floor

b. Nutrition

i. They gain nutrients by filtering particles out of the water

ii. Food particles in the water are trapped and ingested

c. Reproduction

i. asexual - budding

ii. sexual - Sponges are hermaphrodites but produce eggs and sperm at different times to avoid self-fertilization.

3. Phylum Cnidaria

a. General

i. Include jellyfish, sea anemones and corals. Note that although starfish and sea urchins display radial symmetry as adults, they are not in this phylum.

ii. Possess radial symmetry with body parts arranged around a central axis.

iii. Have only two germ layers which give rise to true tissues in the adult body.

iv. Have two body forms

(1) Polyp: cylindrical, generally attached to a substrate (e.g., anemone)

(2) Medusa: umbrella-shaped, free floating, gelatinous (e.g., jellyfish)

b. Nutrition

i. Carnivores which capture food with tentacles surrounding the mouth. Stinging cells (cnidocytes) on tentacles paralyze prey which is then brought into the mouth. The extracellular digestion of food is an evolutionary development.

ii. Food is digested in a gut (gastrovascular cavity) and the resulting particles are absorbed by cells. This allows the animal to digest something larger than it’s own cells.

c. Reproduction

i. Separate sexes jellyfish but lower cnidarians like the hydra show asexual (budding) as well.

4. Phylum Platyhelminthes

a. General

i. Flatworms (e.g., planaria)

ii. The bilateral symmetry allows different body parts to be specialized and cephalization. Cephalization allows animals to move through and experience their environment head first. Sensory equipment is grouped at the anterior end. This is more efficient in seeking food and avoiding danger such as predators.

iii. First appearance of organs - a group of tissues that functions as one unit.

iv. No coelom is present (acoelomate)

v. Body must be thin to allow diffusion of gases and nutrients

b. Nutrition

i. Digestive system is branched with a single opening. Two-way digestive system.

c. Nervous system

i. Primitive eye spots allow planarians to distinguish light and dark.

ii. Beginnings of cephalization.

d. Reproduction

i. Sexual hermaphrodites with the reproductive system only appearing during mating season.

ii. Asexual reproduction can result if the animal is split in two.

5. Phylum Nematoda

a. General

i. Roundworms that live in soil and water. Most are harmless but some are parasites.

ii. Have a body cavity located between endoderm and mesoderm (pseudocoelom)

iii. Importance of the evolution of a body cavity

(1) Circulation - fluids moving within the cavity function as a circulatory system

(2) Movement - fluid in the cavity makes the body rigid

(3) Organ function - organs can function without being deformed

(4) Food movement - not limited by movement of the animal

(5) Digestion and waste removal - can be independent of animal movement.

b. Nutrition

i. Separate mouth and anus - one-way digestive tract

c. Reproduction - sexual with separate males and females

6. Phylum Mollusca

a. General

i. Second largest phylum of animals and second most successful land animals, next to insects. There are more terrestrial mollusks than terrestrial vertebrates.

ii. Includes snails, clams, octopus.

iii. Body cavity (coelom) is completely surrounded by mesoderm.

iv. Coelom allows space for more complex internal organs. Also, digestive tract can be longer than the animal.

v. Also allows larger reproductive system.

vi. Three classes

(1) Class Gastropoda - snails

(2) Class Bivalvia - clams, mussels, oysters, scallops.

(3) Class Cephalopoda - squid, nautilus, octopus.

vii. Clear cephalization except in the bivalves.

b. Nutrition

i. The longer digestive tract with specialized organs allows better digestion and more diverse food.

ii. Bivalves use the gills to filter food particles from the water. Gastropods scrape food from surfaces. Cephalopods are predators.

c. Circulation

i. A large body cavity requires the development of an efficient circulatory system.

ii. A network of vessels carries fluid (blood) to all parts of the body. Blood carries nutrients and oxygen to cells and carries wastes and carbon dioxide away. Circulation is accomplished by the contraction of a muscular heart (or hearts).

iii. Cephalopods have closed circulation.

d. Nervous system - is highly developed in cephalopods because they are predators.

e. Reproduction

i. Most mollusks show sexual reproduction with separate sexes.

ii. Young care is highly developed in the octopus.

7. Phylum Annelida

a. General

i. Segmented worms (e.g., earthworms)

ii. Segmented animals have body built from a series of similar segments. This plan is useful because if one segment of an organ system is damaged, others can replace it. Independent movement of segments allows efficient motility.

iii. The evolutionary advantage is that by changing one segment you can create a new body part without affecting other parts.

iv. Segments can be modified and specialized for various activities.

v. Each segment contains organs for digestion, excretion and locomotion.

vi. Anterior segments are modified to include sensory organs

vii. Note that although segmentation is continued through all other phyla (including humans) it is not always obvious. In arthropods, many arthropod segments are fused together. In humans, segmentation is seen in muscles and in the spine.

viii. Three classes

(1) Class Oligochaeta - earthworms

(2) Class Polychaeta - marine worms

(3) Class Hirudinea - leeches

b. Nutrition - one way digestive system

c. Circulation - closed

d. Reproduction - Sexual, although some show separate sexes while some are hermaphrodites.

8. Phylum Arthropoda

a. General

i. The huge advance in this phylum is the jointed appendage.

ii. Exoskeleton is rigid and made of chitin. It provides protection and limits water loss. The exoskeleton is strong but it’s weight limits the size of arthropods. To become larger, animals require a strong, flexible endoskeleton.

b. Four main classes

i. Class Arachnida - spiders, scorpions, ticks, mites

ii. Class Crustacea - lobsters, crayfish, crabs, shrimps

iii. Classes Diploda and Chilopoda (these are highly segmented, suggesting they are more primitive)

iv. Class Insecta - insects

c. Adaptations for success

i. Segments have specialized functions.

ii. Well defined head with excellent sensory apparatus.

iii. Jointed appendages.

iv. Exoskeleton

d. Digestion

i. Arachnids have no jaws for chewing.

ii. Crustaceans are mostly scavengers with appendages specialized for grasping, chewing, crushing, tearing, etc.

iii. Insects show a wide variety of feeding strategies.

e. Circulation and gas exchange

i. Circulation is open.

ii. Arachnids exchange gases through simple lung. Crustaceans have gills under some of the walking appendages. Insects are quite active and so need a more sophisticated system of gas exchange. They have a system of tubes which open to the outside through which gases can travel.

f. Nervous system

i. Well developed overall. Crustaceans are able to detect tiny vibrations in the water and have compound eyes able to form crude images.

ii. Insects have highly developed sensory gear and most can detect stimuli outside the human range of detection. Most have a few simple eyes and a pair of compound eyes which enable them to form images. They cannot focus well but are excellent for detecting movement. Some insects have tiny hairs which detect air vibrations.

g. Reproduction

i. Separate sexes.

ii. Pheromones are chemicals released by one individual to affect the behaviour of another individual. Sex pheromones are used to attract a mate.

h. Camouflage and coloration

i. Hiding - blend into the environment to evade predators or hide from prey

ii. Attracting attention - bright colors are used to warn potential predators

iii. Mimicry - harmless insects mimic the coloration of a harmful one to avoid being eaten.

i. Social behaviour

i. Termites, bees, ants, and some wasps have complex social systems with specific division of labour.

ii. This makes the colony more efficient by having individuals who specialize in particular tasks.

9. Phylum Chordata

a. General

i. All chordates are in the same phylum - unlike the invertebrates.

ii. Animals with a truly internal endoskeleton.

iii. Four characteristic features

(1) Hollow, dorsal nerve cord

(2) Flexible rod (notochord) along the back of the embryo. Muscles attach to the rod providing flexible locomotion and leads to the possibility of much large animals.

(3) Pharyngeal (gill) slits located behind the mouth

(4) Post-anal tail

iv. Some chordates have lost these features as adults.

b. Vertebrates

i. Possess a backbone. The notochord becomes surrounded and replaced by a bony vertebral column which protect the dorsal nerve cord. The vertebral column allows the body to flex and provides attachment sites for muscles as well as surrounding and protecting the nerve cord.

ii. The endoskeleton is made of bone which is mush stronger than chitin.

(1) All vertebrates have a similar skeletal plan

(2) Fused bones form a skull.

(3) Vertebrae protect the spinal cord.

(4) Ribs extend from some vertebrae to protect internal organs.

(5) Most vertebrates have two pairs of limbs.

iii. The brain is enclosed and protected by a skull.

iv. The sexes are usually separate and reproduction usually sexual.

v. Specialized outer covering - skin, feathers, hair, scales

vi. Large coelom containing vital organs.

vii. Vertebrates have a closed circulatory system.

(1) Evolution of Vertebrate Circulatory System

(a) Vertebrate hearts contain muscular chambers called atria (singular, atrium) and ventricles. Contraction of the chamber forces blood out. Blood flows in one direction due to valves that prevent backflow. The atrium functions to receive blood that is returning to the heart. When it contracts, blood is pumped into the ventricle. The ventricle is the main pumping chamber of the heart. When it contracts, blood is pumped away from the heart to the body, lungs, or gills.

(b) Circulatory System of Fish

(i) Fish have a two-chambered heart with one atrium and one ventricle. The gills contain many capillaries for gas exchange, so the blood pressure is low after going through the gills. Low-pressure blood from the gills then goes directly to the body, which also has a large number of capillaries.

(ii) The activity level of fish is limited due to the low rate of blood flow to the body.

(i) Amphibians have a 3-chambered heart with two atria and one ventricle. Blood from the lungs (pulmonary circuit) goes to the left atrium. Blood from the body (systemic circuit) goes to the right atrium. Both atria empty into the ventricle where some mixing occurs

(ii) The advantage of this system is that there is high pressure in vessels that lead to both the lungs and body.

(d) Circulatory System of Reptiles

(i) In most reptiles, the ventricle is partially divided. This reduces mixing of oxygenated and unoxygenated blood in the ventricle.

(e) Circulatory System of Birds and Mammals

(i) Birds and mammals (also crocodilians) have a four-chambered heart which acts as two separate pumps. After passing through the body, blood is pumped under high pressure to the lungs. Upon returning from the lungs, it is pumped under high pressure to the body.

(ii) The high rate of oxygen-rich blood flow through the body enables birds and mammals to maintain high activity levels. Also, the mixing of oxygenated and deoxygenated blood is prevented.

c. Evolutionary trends in the vertebrates

i. Total dependance on water to a terrestrial lifestyle.

ii. More complex heart.

iii. Increased cephalization.

iv. Increased size and complexity of the cerebrum (for learning and complex behaviour).

d. Class Agnatha - Lamprey eels.

i. The first vertebrates were marine, with tails but without jaws or paired fins.

ii. Have a minimal skeleton made of cartilage.

e. Class Chondrichthyes

i. General - Sharks and rays

(1) Development of the moveable jaw allowed these animals to eat larger prey and become top predators. Teeth are sharp and pointed backward.

(2) Superior, streamlined design for swimming. Moveable, paired fins for propulsion, stabilization and directional movement.

(3) Skeleton made of cartilage.

ii. Nervous system

(1) Very keen sense of smell.

(2) Lateral line allows the sharks to detect vibrations in the water.

iii. Reproduction - is advanced for a fish. Internal fertilization. Eggs generally develop inside the female’s body, and young are born alive.

f. Class Osteichthyes

i. General

(1) Bony fishes developed heavy skeleton made completely of bone. Internal skeleton with backbone surrounding spinal cord. Brain fully encased in a protective skull.

(2) Swim bladder - Gas-filled sac that allows the animal to float suspended at any depth in the water. Sharks must move through the water or sink.

(3) Highly mobile, paired fins are more maneuverable.

(4) Lateral line system - Series of small pits along the animal’s body that can detect objects in the water. The sound receptors of terrestrial vertebrates may have evolved from these organs.

ii. Circulation

(1) Gills extract dissolved oxygen from water around them. Swallowed water passes over filaments rich in blood vessels. Water is then forced out slits in the side of the throat.

(2) Single-loop blood circulation with blood pumped from heart to gills. Oxygenated blood from gills passes to rest of body.

iii. Nervous system

(1) Quite developed to allow for some complex behaviours and movement.

(2) Not great vision but quite a good sense of smell.

iv. Reproduction - separate sexes with mostly external fertilization.

g. Class Amphibia

i. General

(1) Frogs, toads and salamanders

(2) Amphibian were the first to invade the land. They are the first tetrapods. The juvenile part of the life cycle is dependant on water and gas excchange is through gills. The adult part is less dependant on water and gas exchange is through lungs.

ii. Adaptations to live on land

(1) Legs to support body weight and for movement.

(2) Lungs instead of gills because the thin filaments of the gills would clump together out of water.

(3) Improved heart to deliver more oxygen to walking muscles.

(4) Eggs laid in water to prevent them drying out.

(5) Most live close to water to prevent skin from drying out

iii. Circulation and gas exchange

(1) Amphibians have a three chambered heart. This allows more efficient circulation.

(2) Veins return blood from lungs to heart so that oxygenated blood can leave the heart at greater pressure. Because there are only three chambers, oxygenated and deoxygenated blood mix in the ventricle.

(3) Amphibians have small, inefficient lungs and most species also get some oxygen by diffusion through the skin. Because the skin is used in gas exchange it must remain moist, so amphibians can not venture far into very dry habitats.

iv. Reproduction

(1) External fertilization requires that sperm swim through water to the egg so the animals must stay in or near water for reproduction.

(2) The eggs do not have an outer covering or shell and therefore are not protected against drying out.

h. Class Reptilia

i. General - Turtles, crocodiles, alligators, lizards, and snakes.

ii. Adaptations to a fully terrestrial lifestyle

(1) Limbs are directed downward, bent more under the body to raise it up off the ground. This improved support enables reptiles to move more easily and even to run.

(2) Lungs and heart are more efficient.

(3) The skin is waterproof and made from the protein keratin - the same protein in human hair and fingernails and in bird feathers.

(4) Fertilization is internal and the amniotic egg is encased in a water-tight, leathery shell covering.

(5) Reptiles are ectotherms (get their heat from outside their body) and regulate body temperature by behavior - basking in sun or hiding in shade.

iii. Circulation

(1) Heart is four chambered but the ventricles are only partially separated. Crocodilians have a 4 chambered heart. This tends to decrease the mixing of oxygen-poor and oxygen-rich blood in the ventricle, although some still occurs.

(2) Reptiles have more efficient lungs than amphibians. Reptiles do not need to use their skin for gas exchange because the lungs are sufficient. They have a thick, scaly skin with keratin that makes it impermeable to water and gases.

iv. Nervous system

(1) Most have a good sense of smell but poor eyesight.

(2) Most do not have hearing as we think of it. They have membranes on the sides of the head to detect vibrations.

v. Reproduction

(1) Internal fertilization is necessary because reproduction occurs on land. The sperm must be deposited inside the female. Internal fertilization allows animals to mate without having to be in water.

(2) The eggs are encased in leathery shells to protect them from drying out. This eliminates the need for a swimming larval stage.

(3) Amniotic egg - The amniotic egg has several membranes which make it a valuable adaptation for a terrestrial lifestyle. The egg has structures to surround and protect the embryo, provide food, store wastes, and allow oxygen to enter, but retain water.

(4) There is no young care except in crocodilians are only ones to care for young.

i. Class Aves

i. General

(1) Birds

(2) Scales on their legs and feet and claws on their toes are reptilian characteristics.

(3) Beak and feet are adapted to suit the bird’s lifestyle.

(4) Success derived from development of the feather which allows them to fly. Feathers contain the same protein as reptilian skin. They insulate against heat loss and allow birds to be homeotherms (maintain a constant body temperature). Homeothermy allows them to be active when the environmental temperature is low. Birds are endotherms, meaning they get their heat form inside their body.

(5) Anatomical features related to flight

(a) Forelimbs have developed into wings.

(b) Feathers provide lift from the wings.

(d) The skeleton is made of hollow bones to reduce weight.

(e) Enlarged breastbone for attachment of strong flight muscles.

(f) Females have only one ovary.

(g) Efficient respiration - Birds have one-way flow of air through their lungs. As a result, the lungs receive fresh air during inhalation and again during exhalation. During inhalation, the air sacs fill; during exhalation, they empty. Inhaled air goes past the lungs to the air sacs. Air then goes to lungs and is exhaled. Air passes through the lungs in only one direction.

ii. Digestion

(1) Birds eat small amounts of food often and digestion is very fast to minimize the weight during flight.

(2) Birds do not chew and so have no teeth.

iii. Circulation and gas exchange

(1) Birds and mammals have a double circulatory system with 2 atria and 2 ventricles. The double circulatory system is required for the high activity levels seen in birds and mammals as well as being an endotherm.

(2) The four chambered heart allows for an efficient, complete separation of oxygenated and deoxygenated blood.

iv. Nervous system

(1) Highly developed with excellent vision. This is required for flight.

(2) Smell and taste are not as good although hearing is excellent.

(3) The well-developed cerebrum allows for complex behaviour and learning. The cerebellum is also well-developed to allow the complex muscle movements required for flight.

v. Reproduction

(1) Birds have internal fertilization and produce hard-shelled, amniotic eggs.

(2) Birds exhibit complex behavior including parental care.

j. Class Mammalia

i. General

(1) Mammals

(2) Hair

(a) Insulates the body against heat loss. Being endotherms allows activity at any time of day or night in many climates.

(b) Provides camouflage.

(d) May serve as defensive weapons as in porcupines.

(e) Note that marine mammals have blubber in addition to or instead of hair.

(3) Mammary glands

(a) All females possess mammary glands that produce milk for the young. Young are born relatively helpless but are fed milk and cared for by one or both parents.

(b) Milk is rich in fat, sugar, protein with 95% water

(4) Almost all large land vertebrates are mammals although the typical mammal is not large. 3200 of 4100 species are rodents, bats, shrews, or moles.

(5) Mammals have well-developed sense organs and a large brain.

(6) Mammals walk more efficiently than reptiles because their legs are positioned further under their body.

(7) Mammals have a diversity of teeth for different kinds of foods. Fish, amphibians, and reptiles have teeth that are all similar.

ii. Circulation

(1) Mammals (like birds) have a four-chambered heart, and separate pulmonary (lung) and systemic (body) circulatory systems.

(2) More efficient breathing results from diaphragm breathing muscle.

iii. Reproduction

(1) Monotremes - egg-laying mammals which include the duck-billed platypus and spiny anteater. Unlike other mammals, monotremes lay eggs which the female incubates. They do not have nipples but milk is secreted to the surface of the skin.

(2) Marsupials - pouched-mammals which includes opossums, kangaroos, and koalas in addition to some mouse and wolf relatives in Australia. Marsupial young begin development in the female’s body. They are born very immature (in as few as eight days after fertilization) and crawl into the mother’s pouch. There they attach to nipples and continue to develop.

(3) Placenta

(a) Most mammals are placental and give birth to live young.

(b) Fetus can get nutrients from the mother’s blood stream through the placenta.

(d) Placental mammals are born relatively mature because the well-developed placenta for nutrient and waste exchange enables them to remain within the mother for an extended period of development.